From: Thierry Reding <thierry.reding@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Olof Johansson <olof@lixom.net>, Rob Herring <robh+dt@kernel.org>,
Pawel Moll <Pawel.Moll@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Kumar Gala <galak@codeaurora.org>,
Stephen Warren <swarren@wwwdotorg.org>,
Arnd Bergmann <arnd@arndb.de>, Will Deacon <Will.Deacon@arm.com>,
Joerg Roedel <joro@8bytes.org>,
Cho KyongHo <pullip.cho@samsung.com>,
Grant Grundler <grundler@chromium.org>,
Dave P Martin <Dave.Martin@arm.com>,
Marc Zyngier <Marc.Zyngier@arm.com>,
Hiroshi Doyu <hdoyu@nvidia.com>,
Olav Haugan <ohaugan@codeaurora.org>,
Varun Sethi <varun.sethi@freescale.com>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4] devicetree: Add generic IOMMU device tree bindings
Date: Thu, 31 Jul 2014 12:09:06 +0200 [thread overview]
Message-ID: <20140731100905.GA7458@ulmo> (raw)
In-Reply-To: <20140730181842.GG20162@leverpostej>
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On Wed, Jul 30, 2014 at 07:18:42PM +0100, Mark Rutland wrote:
[...]
> > >> +
> > >> +Multiple-master IOMMU with configurable DMA window:
> > >> +---------------------------------------------------
> > >> +
> > >> + / {
> > >> + #address-cells = <1>;
> > >> + #size-cells = <1>;
> > >> +
> > >> + iommu {
> > >> + /* master ID, address and length of DMA window */
> > >> + #iommu-cells = <4>;
> > >> + };
> > >> +
> > >> + master {
> > >> + /* master ID 42, 4 GiB DMA window starting at 0 */
> > >> + iommus = <&/iommu 42 0 0x1 0x0>;
> > >
> > > Is this that window is from the POV of the master, i.e. the master can
> > > address 0x0 to 0xffffffff when generating transactions, and these get
> > > translated somehow?
> > >
> > > Or is this the physical addresses to allocate to the master?
> >
> > It needs to be clarified in the documentation, but as far as I know it
> > is the DMA address space that is used.
>
> Ok. So that's pre-translation, from the POV of the master?
Correct. It represents the window of the IOMMU's addressable I/O virtual
address space that should be assigned to this particular master.
> If we don't have that knowledge about the master already (e.g. based on
> the compatible string), surely we always need that information in a
> given iommu-specifier format? Otherwise certain iommus won't be able to
> handle masters with limited addressing only due to limitations of their
> binding.
This is only used for what's often called a windowed IOMMU. Many IOMMUs
(non-windowed) typically allow only a complete address space to be
assigned to a master without additional control over subregions. So this
is really a property/capability of the IOMMU rather than the masters
themselves.
There are already other means to respect the addressing limitations of
masters. We typcially use a device's DMA mask for this, and it's natural
to reuse that for I/O virtual addresses since they will in fact take the
place of physical addresses for the master when translation is enabled.
Thierry
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next prev parent reply other threads:[~2014-07-31 10:09 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-04 15:29 [PATCH v4] devicetree: Add generic IOMMU device tree bindings Thierry Reding
2014-07-09 13:40 ` Will Deacon
2014-07-09 14:21 ` Thierry Reding
2014-07-09 18:10 ` Will Deacon
2014-07-10 9:49 ` Thierry Reding
2014-07-10 10:23 ` Will Deacon
2014-07-10 10:57 ` Thierry Reding
2014-07-10 12:38 ` Will Deacon
2014-07-11 20:55 ` Rob Clark
2014-07-12 9:39 ` Will Deacon
2014-07-12 11:26 ` Rob Clark
2014-07-12 12:22 ` Arnd Bergmann
2014-07-12 12:57 ` Rob Clark
2014-07-13 9:43 ` Will Deacon
2014-07-13 11:43 ` Rob Clark
2014-07-16 1:25 ` Olav Haugan
2014-07-16 10:10 ` Will Deacon
2014-07-16 20:24 ` Rob Clark
2014-07-14 6:44 ` Thierry Reding
2014-07-14 10:08 ` Will Deacon
2014-07-14 6:24 ` Thierry Reding
2014-07-14 10:13 ` Rob Clark
2014-07-14 6:15 ` Thierry Reding
2014-07-30 11:04 ` Will Deacon
2014-07-30 13:23 ` Thierry Reding
2014-07-30 13:33 ` Joerg Roedel
2014-07-30 17:37 ` Olof Johansson
2014-07-30 14:30 ` Will Deacon
2014-07-30 18:08 ` Rob Herring
2014-07-30 20:11 ` Arnd Bergmann
2014-07-30 15:26 ` Mark Rutland
2014-07-30 17:35 ` Olof Johansson
2014-07-30 18:18 ` Mark Rutland
2014-07-31 10:09 ` Thierry Reding [this message]
2014-07-31 10:50 ` Mark Rutland
2014-07-31 11:14 ` Thierry Reding
2014-07-31 9:51 ` Thierry Reding
2014-07-31 8:39 ` Thierry Reding
2014-07-31 9:22 ` Mark Rutland
2014-07-31 10:18 ` Thierry Reding
2014-07-31 10:23 ` Joerg Roedel
2014-07-31 10:46 ` Thierry Reding
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